Metals, determination graphite furnace atomic absorption spectrometry

Trace metals in sea water are preconcentrated either by coprecipitating with Ee(OH)3 and recovering by dissolving the precipitate or by ion exchange. The concentrations of several trace metals are determined by standard additions using graphite furnace atomic absorption spectrometry. 

Many of the published methods for the determination of metals in seawater are concerned with the determination of a single element. Single-element methods are discussed firstly in Sects. 5.2-5.73. However, much of the published work is concerned not only with the determination of a single element but with the determination of groups of elements (Sect. 5.74). This is particularly so in the case of techniques such as graphite furnace atomic absorption spectrometry, Zeeman background-corrected atomic absorption spectrometry, and inductively coupled plasma spectrometry. This also applies to other techniques, such as voltammetry, polarography, neutron activation analysis, X-ray fluroescence spectroscopy, and isotope dilution techniques. 

Statham [448] has optimised a procedure based on chelation with ammonium dithiocarbamate and diethylammonium diethyldithiocarbamate for the preconcentration and separation of dissolved manganese from seawater prior to determination by graphite furnace atomic absorption spectrometry. Freon TF was chosen as solvent because it appears to be much less toxic than other commonly used chlorinated solvents, it is virtually odourless, has a very low solubility in seawater, gives a rapid and complete phase separation, and is readily purified. The concentrations of analyte in the back-extracts are determined by graphite furnace atomic absorption spectrometry. This procedure concentrates the trace metals in the seawater by a factor of 67.3. 

Cadmium, copper, and silver have been determined by an ammonium pyrrolidine dithiocarbamate chelation, followed by a methyl isobutyl ketone extraction of the metal chelate from the aqueous phase [677], and finally followed by graphite furnace atomic absorption spectrometry. The detection limits of this technique for 1% absorption were 0.03 pmol/1 (copper), 2 nmol/1 (cadmium), and 2 nmol/1 (silver). 

Tominaga et al. [682,683] studied the effect of ascorbic acid on the response of these metals in seawater obtained by graphite-furnace atomic absorption spectrometry from standpoint of variation of peak times and the sensitivity. Matrix interferences from seawater in the determination of lead, magnesium, vanadium, and molybdenum were suppressed by addition of 10% (w/v) ascorbic acid solution to the sample in the furnace. Matrix effects on the determination of cobalt and copper could not be removed in this way. These workers propose a direct method for the determination of lead, manganese, vanadium, and molybdenum in seawater. 

Mykytiuk et al. [184] have described a stable isotope dilution sparksource mass spectrometric method for the determination of cadmium, zinc, copper, nickel, lead, uranium, and iron in seawater, and have compared results with those obtained by graphite furnace atomic absorption spectrometry and inductively coupled plasma emission spectrometry. These workers found that to achieve the required sensitivity it was necessary to preconcentrate elements in the seawater using Chelex 100 [121] followed by evaporation of the desorbed metal concentrate onto a graphite or silver electrode for isotope dilution mass spectrometry. 

Other applications of supported liquid membranes have been related to metal speciation. For example, recently a system for chromium speciation has been developed based on the selective extraction and enrichment of anionic Cr(VI) and cationic Cr(III) species in two SLM units connected in series. Aliquat 336 and DEHPA were used respectively as carriers for the two species and graphite furnace atomic absorption spectrometry used for final metal determination. With this process, it was possible to determine chromium in its different oxidation states [103]. 

Both flame and graphite furnace atomic absorption spectrometry are two of the commonest techniques used for the determination of metals and metalloids. Various authors " have discussed the application of both to the analysis of trace elements in biological materials. 

The recommended procedure for the determination of arsenic and antimony involves the addition of 1 g of potassium iodide and 1 g of ascorbic acid to a sample of 20 ml of concentrated hydrochloric acid. This solution should be kept at room temperature for at least five hours before initiation of the programmed MH 5-1 hydride generation system, i.e., before addition of ice-cold 10% sodium borohydride and 5% sodium hydroxide. In the hydride generation technique the evolved metal hydrides are decomposed in a heated quartz cell prior to determination by atomic absorption spectrometry. The hydride method offers improved sensitivity and lower detection limits compared to graphite furnace atomic absorption spectrometry. However, the most important advantage of hydride-generating techniques is the prevention of matrix interference, which is usually very important in the 200 nm area. 

A number of methods have been described for determining the concentrations of toxic metals in biological samples.These methods include graphite furnace atomic absorption spectrometry (GF-AAS), electroanalytical techniques such as anodic stripping voltammetry (ASV), neutron activation analysis (NAA), and mass spectrometry (MS). Amongst these techniques, mass spectrometry occupies a unique role due to its potential to measure the... 

Other publications with a sample treatment component of relevance are those by Burguera et al. (1995, Determination of iron and zinc by on-line microwave-assisted mineralization and flow-injection graphite furnace atomic absorption spectrometry) Torres et al. (1995, Microwave-assisted robotic method for the determination of trace metals in soil) and Burguera et al. 

Based on the principles of precipitate flotation, a rapid and convenient separation technique has been developed for the determination of toxic heavy metals adsorbed on suspended solids in freshwater. Because suspended solids are negatively charged species, they are rendered hydrophobic and coagulate to form bulky floes with a cationic surfactant and sodium chloride (to increase the ionic strength). The floes are easily floated by bubbling and are then treated in nitric acid to determine the desorbed heavy metals (e.g., chromium, manganese, copper, cadmium, and lead) by graphite furnace atomic absorption spectrometry. 

Nakashima, S. Sturgeon, R.E. Willie, S.N. Berman, S.S. Determination of trace metals in seawater by graphite furnace atomic absorption spectrometry with preconcentration on silica-immobilized 8-hydroxyquinoline in a flow-system. Fresenius Z. Anal. Chem. 1988, 330 (7), 592. 

R.E. Sturgeon, S.S. Berman, A. Desaulniers, and D.S. Russell. Pre-concentration of trace metals from sea-water for determination by graphite-furnace atomic-absorption spectrometry. Talanta 27 85-91,1980. 

M. Tiizen. Determination of heavy metals in fish samples of the middle Black Sea (Turkey) by graphite furnace atomic absorption spectrometry. Food Chemistry 80 119-123, 2003. 

The need for the determination of metallic constituents or impurities in pharmaceutical products has, historically, been addressed by ion chromatographic methods or various wet-bench methods (e.g. the USP heavy metals test). As the popularity of atomic spectroscopy has increased, and the equipment has become more affordable, spectroscopy-based techniques have been routinely employed to solve analytical problems in the pharmaceutical industry. Table 1 provides examples of metal determinations in pharmaceutical matrices, using spectroscopic techniques, and the reasons why these analyses are important. Flame atomic absorption spectrometry (FAAS), graphite furnace atomic absorption spectrometry... 

ASTM (2002) D1971-02 Standard Practices for Digestion of Water Samples for Determination of Metals by Flame Atomic Absorption, Graphite Furnace Atomic Absorption, Plasma Emission Spectroscopy, or Plasma Mass Spectrometry. ASTM International. For referenced ASTM standards, visit the ASTM website www.astm.org. 

Cruz, R. B. and Loon, J. C. van "A Critical Study of the Application of Graphite-Furnace Non-Flame Atomic Absorption Spectrometry to the Determination of Trace Base Metals In Complex Heavy-Matrix Sample Solutions". Anal. Chlm. Acta (1974), 72, 231-243. 

Bruland et al. [122] have shown that seawater samples collected by a variety of clean sampling techniques yielded consistent results for copper, cadmium, zinc, and nickel, which implies that representative uncontaminated samples were obtained. A dithiocarbamate extraction method coupled with atomic absorption spectrometry and flameless graphite furnace electrothermal atomisation is described which is essentially 100% quantitative for each of the four metals studied, has lower blanks and detection Emits, and yields better precision than previously published techniques. A more precise and accurate determination of these metals in seawater at their natural ng/1 concentration levels is therefore possible. Samples analysed by this procedure and by concentration on Chelex 100 showed similar results for cadmium and zinc. Both copper and nickel appeared to be inefficiently removed from seawater by Chelex 100. Comparison of the organic extraction results with other pertinent investigations showed excellent agreement. 

Danish Standard (1990) Determination of metals in water, sludge and sediments - determined by flameless for determination by atomic absorption spectrometry - electrothermal atomisation in graphite furnace - General principles and guidelines. Ds 2210. 

Electrothermal atomic absorption spectrometry (ETAAS) has been the single most important technique in advancing our knowledge of the transition metal distribution in seawater. The graphite-furnace mode is used most frequently. It has the advantage of high sensitivity and therefore small sample volume (e.g., 10-50//L). Major disadvantages are the matrix interferences which usually necessitate a pre-concentration and/or a separation step (see Sections 12.2.1 and 12.2.2). Another application of ETAAS is the cold-vapour technique for the determination of mercury (Section 12.2.4). 

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